21020681 has 4 divisors (see below), whose sum is σ = 22931664. Its totient is φ = 19109700.

The previous prime is 21020651. The next prime is 21020683. The reversal of 21020681 is 18602012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21020681 - 2⁶ = 21020617 is a prime.

It is a super-2 number, since 2×21020681² = 883738059407522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21020683) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 955475 + ... + 955496.

It is an arithmetic number, because the mean of its divisors is an integer number (5732916).

Almost surely, 2^21020681 is an apocalyptic number.

It is an amenable number.

21020681 is a deficient number, since it is larger than the sum of its proper divisors (1910983).

21020681 is a wasteful number, since it uses less digits than its factorization.

21020681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1910982.

The product of its (nonzero) digits is 192, while the sum is 20.

The square root of 21020681 is about 4584.8316217719. The cubic root of 21020681 is about 275.9829550840.

Adding to 21020681 its reverse (18602012), we get a palindrome (39622693).

The spelling of 21020681 in words is "twenty-one million, twenty thousand, six hundred eighty-one".